There is no ranking in currency. You have to choose the criteria you base your ranking on. For examole if it is about how big the market size is or the value of the currency bitcoin is number one but that isn't true when talking about the profit margin because there maybe other currencies that will make you more money if you invest in them.
Yes it depends on our criteria,if we are looking in terms of its orice then bitcoin is the most expensive currency ever but the fact is we are not using bitcoin as our currency we just using it as trading material so still it is not in the rank one when compared to fiat money ij trrms of usage.